As a technology for preventing a collision between vehicles, a technology that monitors a distance between the vehicles by using various pieces of information acquired by using sensors including an ultrasonic sensor, and the like and warns a driver when the distance between the vehicles is smaller than a set distance value is adopted in a lot of vehicles. However, in the case of preventing the collision between the vehicles depending only on the sensor, it is difficult to measure the distance between the vehicles under various driving environments, and as a result, an inaccurate result may be measured.
In recent years, a technology that acquires information on a surrounding situation of a vehicle, which is driven, by various methods other than the sensors and warns the driver when the distance between the vehicles is short based on the acquired information is being researched.